WO2023107436A2

WO2023107436A2 - Wastewater treatment process

Info

Publication number: WO2023107436A2
Application number: PCT/US2022/051941
Authority: WO
Inventors: Scott Lee BERGGREN; Paul Stanton KENNEDY; Brajendra Mishra; Himanshu TANVAR
Original assignee: Grön Metallic Group, Inc.
Priority date: 2021-12-06
Filing date: 2022-12-06
Publication date: 2023-06-15
Also published as: WO2023107436A3

Abstract

A wastewater treatment process that contemplates providing a mix of mineral oxides and contacting the mix with wastewater that contains at least one heavy metal. The mix removes at least some of the at least one heavy metal from the wastewater.

Description

Wastewater Treatment Process

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of Provisional Patent Application US 63/286,416, filed on December 6, 2021, the entire disclosure of which is incorporated by reference herein for all purposes.

BACKGROUND

[0002] This disclosure relates to a process for treating wastewater that contains heavy metals.

[0003] Properly treating wastewater that contains heavy metals is expensive and typically requires a lot of resources.

SUMMARY

[0004] The present disclosure relates to a process for the treatment of wastewater, to remove at least heavy metals. In the process a mix of mineral oxides is provided. This mix is then contacted with wastewater that contains at least one heavy metal. The mix removes at least some of the heavy metals from the wastewater. Aspects and examples are directed to a process for treating wastewater that contains heavy metals. Solid mixed mineral oxides can be used to remove heavy metals from the wastewater.

[0005] All examples and features mentioned below can be combined in any technically possible way.

[0006] In one aspect, a wastewater treatment process includes providing a mix of solid mineral oxides, and contacting the solid mineral oxide mix with liquid wastewater that contains at least one heavy metal. The solid mineral oxide mix removes at least some of the heavy metal from the wastewater.

[0007] Some examples include one of the above and/or below features, or any combination thereof. In an example the solid mineral oxide mix comprises calcined bauxite residue (CBR). In an example the process further includes processing in a furnace the solid mineral oxide mix after it has been contacted with the wastewater, to reduce its oxide content and recover metallic iron. In an example the process is effective to remove at least some of one or more of cadmium, chromium, arsenic, and mercury in the wastewater.

[0008] Some examples include one of the above and/or below features, or any combination thereof. In an example a ratio of solid to liquid in the contacting step is at least 1 : 10. In an example the ratio of solid to liquid is at least 2: 10. In an example the process is effective to remove at least 95% of at least one heavy metal in the liquid wastewater. In some examples the pH of the liquid wastewater is reduced before the contacting step, to lower the pH of the solid mineral oxide mix during its contact with the liquid wastewater, to increase the effectiveness of heavy metal removal. In an example the pH of the liquid wastewater is reduced to from about 2 to about 3.

[0009] Some examples include one of the above and/or below features, or any combination thereof. In some examples the solid mineral oxide mix comprises or is made up of calcined bauxite residue (CBR). In some examples the process further includes processing in a furnace the solid mineral mix residue after it has been contacted with the wastewater, to reduce its oxide content and recover metallic iron. In an example the furnace process comprises reducing the solid mineral mix residue with a reducing agent at a temperature of from about 500°C to about 600°C. In an example the reducing agent comprises a source of solid carbon. In an example the process further includes adding a coagulant to the wastewater. In an example the coagulant comprises calcium oxide. In an example the process further includes washing the solid mineral oxide with acid before the contacting step, to reduce its pH and reduce the levels of Na and Ca.

[0010] In another aspect, a wastewater treatment process includes providing a mix of solid mineral oxides that comprises calcined bauxite residue (CBR), contacting the solid mineral oxide mix with liquid wastewater that contains at least one heavy metal, wherein the solid mineral oxide mix removes at least some of the heavy metal from the wastewater, and processing in a furnace the solid mineral oxide mix after it has been contacted with the wastewater, to reduce its oxide content and recover metallic iron. The process is effective to remove at least some of one or more of cadmium, chromium, arsenic, and mercury in the wastewater. [0011] Some examples include one of the above and/or below features, or any combination thereof. In an example the process further includes washing the solid mineral oxide with acid before the contacting step, to reduce its pH and reduce the levels of Na and Ca. In an example the process is effective to remove at least some of one or more of cadmium, chromium, arsenic, and mercury in the wastewater. In an example a ratio of solid to liquid in the contacting step is at least 1 : 10. In an example the furnace process comprises reducing the solid mineral mix residue with a reducing agent at a temperature of from about 500°C to about 600°C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Various aspects of at least one example are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and examples, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the inventions. In the figures, identical or nearly identical components illustrated in various figures may be represented by a like reference character or numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

[0013] Fig 1 is flow chart of a wastewater treatment process.

[0014] Figures 2A and 2B present data for fixed beds. Figures 2C and 2D present data for stirring. Figures 2E and 2F present data for shaking (mixing).

[0015] Figures 3 A and 3B present data for stirring, but for Cd.

[0016] Figures 4, 5 A and 5B present data for mixed solution of Cd, As, Cr Hg, pH = 1 (Fig. 4) and pH 2 (Figs. 5A and 5B).

[0017] Figure 6 presents data for mixed solution of Cd, As, Cr, Hg, pH = 2, Material - CBR (different solid to liquid ratios).

[0018] Figures 7A-7E present data for individual testing of metals (As, Cr, Hg, Pb, Cd) 100 ppm starting concentration, Ih time (fixed). [0019] Figures 8A-8F present data for metal solutions with different starting concentrations (5, 50, 100 ppm). Solid-liquid ratio fixed at O. lg/ml.

DETAILED DESCRIPTION

[0020] Examples of the systems, methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The systems, methods and apparatuses are capable of implementation in other examples and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, functions, components, elements, and features discussed in connection with any one or more examples are not intended to be excluded from a similar role in any other examples.

[0021] Examples disclosed herein may be combined with other examples in any manner consistent with at least one of the principles disclosed herein, and references to “an example,” “some examples,” “an alternate example,” “various examples,” “one example” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one example. The appearances of such terms herein are not necessarily all referring to the same example.

[0022] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to examples, components, elements, acts, or functions of the computer program products, systems and methods herein referred to in the singular may also embrace embodiments including a plurality, and any references in plural to any example, component, element, act, or function herein may also embrace examples including only a singularity. Accordingly, references in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. Process Overview

[0023] A ‘closed loop’ process that will treat industrial wastewater for the removal of hazardous heavy metals and other water contaminants utilizing a mix of mineral oxides. See Figure 1 for a process overview. In some examples the mixed mineral oxides have a minimum Fe3O4 content of about 30%. In some examples the process avoids disposal of the spent mineral oxides after the adsorption of the contaminants by utilizing a furnace to reduce the oxides into one or more metallic elements, which can then be recovered. In some examples a calcined bauxite residue (CBR) is used as one of those mixed mineral compounds for the process. Or, CBR can be the only source of mineral oxides.

[0024] In an example the process starts with the use of a specialized compound of mixed mineral oxides used to remove heavy metals from wastewater. Known (and proven) effective mineral oxides for this application include; Fe3O4, A12O3, TiO2, SiO, MgO, and others. This mixed mineral compound can be assembled with additional specific components to achieve specific water treatment goals.

[0025] An alternative to assembling the specific components such as oxides in a compound, is utilizing ‘calcined bauxite residue’ minerals (CBR) that already contains a mix of minerals known to be effective in the removal of heavy metals from water. CBR consists of several mineral oxides. Typically, CBR is produced by reducing bauxite residue with a reducing agent (e.g., carbon) at a temperature of 500-600°C. The process results in transformation/reduction of hematite (Fe2O3) present in the raw bauxite residue to magnetite (Fe3O4) in the CBR. Although all CBRs do not have the same mineral oxides in the same proportion, in one example CBR includes Fe3O4 (40%), A12O3 (25%), TiO2 (5%), SiO2 (9%), MgO (1%) and others. The mineral content of CBRs varies, at least in part based on location and the source of the bauxite. CBR can also be amended with specific minerals for added performance effects.

[0026] When the wastewater is combined with the mixed mineral compound, the compound acts to adsorb the hazardous heavy metals, and in some cases may also act as a coagulant that helps the CBR/heavy metal substances to settle more easily, which promotes their separation from the cleaned water. CBR may act as a coagulant since it has some Fe material that can help the solids coagulation during water treatment.

[0027] In water treatment, the contaminant typically adheres to the surface of the pores of the sorptive material. Depending on the material, the pores can be meso, macro, or micro. Activated carbon, which is a common sorptive material, has more micropores. CBR typically comprises meso and macro pores that make it adsorptive of heavy metals and other species such as some organics, similar to the effects of activated carbon. The metals removal likely happens on the surface of the mineral compounds since it involves chemical reactions as opposed to physical adsorption. Physical sorption happens mostly in the pores and on the surface to some extent. Organic chemical removal is likely as physical adsorption, while metals, as chemisorption.

[0028] In some examples a common flocculent such as calcium carbonate can be added, as depicted in Fig. 1. In some examples a separate coagulant (such as CaO) can also or alternatively be added to improve the settling of CBR after water treatment. In some cases, 100% of the heavy metals or close to 100% can be removed from the water, or they can be reduced to a dramatically lower content - making the water acceptable for reuse or safe disposal. Data are presented below and in the figures.

[0029] The spent CBR (with the adsorbed heavy metals) would need to be disposed of. In some examples disposal is accomplished without traditional disposal methods. The spent CBR can be processed in a furnace to reduce the oxide content in the CBR compounds and recover metallic iron in the form of pig iron. When reduced in a furnace, a small portion of some of the elemental metals in the spent CBR would follow the metallic Fe into solution (Cd, Cr, As, Hg, Pb, other), but none in amounts that would affect the chemistry or use of the metallic iron recovered when used as pig iron. The non-reducible oxides would also go into the slag (along with the Al and Ti), and a small portion would be vaporized during the melt.

[0030] The furnace treatment is a carbo-thermic reduction process that is well-known to those skilled in the art of smelting metal bearing ores. This process will remove the oxygen from metal oxides by heating it with carbon at a high temperature. The reduction produces gaseous carbon monoxide which is burned inside the furnace melting zone to produce additional heat. Gaseous carbon dioxide is exhausted into the atmosphere or captured for other uses. The metal oxides which cannot be reduced by reaction with carbon should be melted to a liquid condition to improve their ease of separation from the liquid iron in the furnace. Due to the lower density of the slag, it will always float on top of the liquid (or solid) iron. The melting temperature of these non-reducible oxides can be substantially depressed by the addition of alkaline fluxes such as calcium oxide, sodium oxide and magnesium oxide and their carbonates. At this point the slag is ‘safe’ for regular disposal or for grinding and use, for example, in construction and road fill materials. The slag could also be further processed for the extraction of the individual components in the slag - provided it presented an economic benefit.

[0031] The design of the furnace is well known by those skilled in the art of smelting and can be built to operate with either fossil fuels or electric power.

[0032] A series of experiments were run to determine substances that are removed from water by mixed mineral oxides, such as CBR. In experiment 1, 200 ml stock solution was allowed to flow by gravity through a powder bed containing 200 g of CBR. The filtration was very slow and so was allowed to run overnight to pass all the solution. In experiment 2, 200 ml stock solution was flowed through a powder bed of 80 g CBR; the filtration speed was increased by connecting to a vacuum pump. Total time of filtration was Ih. In experiment 3, bauxite residue (BR) was used instead of CBR. Otherwise, the conditions were the same as experiment 2. Results are presented in Table 1 below.

Table 1

Concentration of stock solution and solution after passing over CBR and raw Bauxite Residue (BR)

[0033] A separate experiment aimed at determining phosphate removal was conducted. The water before and after filtration was analyzed for Phosphorous (P), but the P in solution is present as Phosphate (PO43-) so P indirectly represents phosphate. The solution was made by dissolving disodium hydrogen phosphate (Na2HPO4), which dissolves in solution as Phosphate Ions (HPO4-2 and PO4-3). ICP testing analyzed metal (such as P) but it's normally present as some compound in the solution (e.g., phosphate, PO4 here). The testing had the following results (Table 2) , where P concentrations were determined by ICP testing.

Table 2

[0034] In another experiment CBR was used at 80 pounds per 1000 gallons of contaminated water. Results are shown in Table 3 below.

Table 3

[0035] The CBR consists of some alkali oxides that includes oxides of Na and Ca. The bulk pH of the CBR is typically about 10-11. Acid washing (e.g., using HC1) can be conducted, to help in neutralizing the CBR (if required) prior to the water treatment. Acid washing reduces Na and Ca levels in the CBR, which might be done if their levels are higher than acceptable, or to reduce their levels in the resulting wastewater. Water treatment using CBR without acid neutralization can cause transfer of alkali from CBR to the treated water. If that is not desired, CBR can be neutralized with acid prior to using for water treatment to separate alkali beforehand. However, acid washing can have an impact on metal removal capacity as highlighted in Table 4. Also, the pH of the liquid wastewater can be reduced to an acidic range (e.g., pH of around 2 to around 3) before the addition of CBR. This will lower the pH of the solid mineral oxide mix during its contact with the liquid wastewater, which can make metals removal by the CBR more effective.

Table 4

HC1 washing of Reduced/Calcined BR (CBR)

Conditions - I M HC1, 13% S/L, 15 min (same as optimized conditions for bauxite residue)

[0036] Table 5 gives data that presents removal differences with acid washed CBR and acid washed BR. Data includes concentration of stock solution, and solution after passing over HC1 washed CBR and HC1 washed BR. Both experiments used 200 mL stock solution, powder bed using 80 g sample. Used a vacuum pump to increase filtration time.

Table 5

Observations:

[0037] Comparison of experiments 1 and 2 establish that the treatment is sensitive to time of exposure for a given reagent/water ratio. This factor can be optimized relative to other process conditions. The CBR mineral works w^?ell for removal of heavy metals - Cd, Cr, As and Hg. Controlled levels of Na and Ca may be acceptable for clean water. Calcium can be lowered by CO2 bubbling.

[0038] Additional data and test results are presented in Figures 2-8.

[0039] Figures 2A and 2B present data for As removal using fixed beds of adsorbent. Figures 2C and 2D present data for As removal using stirring of the adsorbent. Figures 2E and 2F present data for As removal using shaking (mixing) of the adsorbent.

[0040] Figures 3 A and 3B present data for adsorbent stirring, but for Cd.

[0041] Figures 4, 5 A and 5B present data for a mixed solution of Cd, As, Cr Hg at pH = 1 (Fig. 4) and pH 2 (Figs. 5A and 5B). Material - reduced/calcined BR, bauxite residue (Ig/lOml).

[0042] Figure 6 presents data for mixed solution of Cd, As, Cr, Hg at pH = 2, Material - CBR (different solid to liquid ratios). [0043] Figures 7A-7E present data for individual testing of metals (As, Cr, Hg, Pb, Cd) 100 ppm starting concentration. Ih time (fixed).

[0044] Figures 8A-8F present data for different metal solutions with different starting concentrations (5, 50, 100 ppm), pH 2, and different contact times. Solid-liquid ratio fixed at O. lg/ml.

[0045] Following are some observations from these data. Comparison of Exp. 1 and 2 show that the treatment is sensitive to time of exposure for a given reagent/water ratio. This factor can be optimized. The CBR works well for removal of heavy metals -• Cd, Cr, As and Hg. Controlled levels of Na and Ca may be acceptable for clean water. Calcium can be lowered by CO2 bubbling.

[0046] Following are alternative scenarios for different wastewaters that can be treated using this process. One proven application for CBR is its effective use as a filter media for the adsorption of heavy metals. This application could be applied to the treatment of Canadian (or other) oil sands process water (OSPW). Oil sands process water is the spent water utilized in the fracking process to recover oil. In fracking, fresh water is used to oil extraction process form the ground. The oil sands industry consumes roughly three barrels of fresh water for every barrel of oil produced. Process water generally cannot be reused. Companies are forced to truck the water for disposal. The process water is typically disposed of (stored) in containment ponds or put into deep holes for disposal. The use of fresh water and storage of contaminated water also carries a logistic nightmare. Hundreds of trucks in and hundreds of trucks out are common for a fracking area.

[0047] The residual water contains large amounts of heavy metals (As, Cd, Cr, Pb and other) that prevent the water from being disposed of in conventional manners. As a result, drilling companies have to collect and store the water in numerous containment ponds.

[0048] It is estimated that several hundred billion gallons of oil sands process water (OSPW) are being stored in Canada, creating a long-term environmental concern. Because of the mounting gallons of water being stored, recent thought has been given to discharging the water in various rivers for disposal. This option is catastrophic to the environmental and ecological footprint of the region.

[0049] Because of the on-going and growing disposal problem of the process water, new legislation in Alberta is allowing for the ‘controlled release’ of tailing ponds into the environment. New regulations which go into effect in 2022 will allow companies to release 1.3 trillion liters of liquid waste into the Athabasca River.

[0050] The calcined bauxite mineral (CBR) can be used for treating the water to remove and/or reduce the toxic levels of heavy metals, allowing for safe discharge or even reuse of the water. The spent CBR (with the adsorbed heavy metals) would need to be disposed of. The spent CBR can be processed in a furnace to reduce the oxide content in the CBR compound, and recover metallic iron in the form of pig iron. The furnace process is described above.

[0051] The pig iron can be sold to steel mills for making product. The slag can be ground and utilized for roadbeds, or potentially put through another process for further material recovery (depending on the chemistry content, and provided a value was realized). An example is recovery of rare earth elements.

[0052] Key Points and Results to Date:

• Bauxite Residue is eliminated as a hazardous industrial waste.

• Oil Sands/Frac Process Water is cleaned and restored to a manageable content.

• The need to dispose of the CBR adsorption material is replaced by a process to convert the mineral compound into recoverable products for use/sale.

• Adding CaO to the clarifier with the CBR will help the adsorbed CBR media settle to the bottom of the clarifier for removal and benefit the sludge content when utilized in the furnace reduction to produce metallic iron. (CaO is a fluxing additive that can be useful in the reduction process).

• The CBR filter media with a pH of around 10 will help lower the acidic level of the water being treated.

• The CBR mineral outperforms raw bauxite residue in the removal of heavy metals from water. Initial tests have shown that a ratio of 1.5: 10 (1.5 parts mineral: 10 parts water) will remove 100% of Cd and As (Cd and As starting content 110 pm each).

[0053] In another example, the subject process can be used to clean other mining and tailing ponds to remove heavy metals. One example is treatment of gold mine process water, for example for removal of one or both of As and Cd.

[0054] In sum, this disclosure features a process to manage and remediate mineral tailings that further utilizes the remediated minerals for the application of removing Heavy Metals and Inorganic Elements/Compounds from Industrial Wastewater, and further processing of these utilized minerals after water treatment for a no landfill disposal. The mineral compound used in water treatment applications has shown in current process testing that it can remove 100% of certain heavy metal elements from water (Cd and As) and near 100% on others (Hg, Pb, Cr, P and others).

[0055] Having described above several aspects of at least one example, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only, and the scope of the invention should be determined from proper construction of the appended claims, and their equivalents.

Claims

What is claimed is:

1. A wastewater treatment process, comprising: providing a mix of solid mineral oxides; and contacting the solid mineral oxide mix with liquid wastewater that contains at least one heavy metal, wherein the solid mineral oxide mix removes at least some of the heavy metal from the wastewater.

2. The process of claim 1, wherein the solid mineral oxide mix comprises calcined bauxite residue (CBR).

3. The process of claim 1, further comprising processing in a furnace the solid mineral oxide mix after it has been contacted with the wastewater, to reduce its oxide content and recover metallic iron.

4. The process of claim 1, wherein the process is effective to remove at least some of one or more of cadmium, chromium, arsenic, and mercury in the wastewater.

5. The process of claim 1, wherein a ratio of solid to liquid in the contacting step is at least 1 : 10.

6. The process of claim 5, wherein the ratio of solid to liquid is at least 2: 10.

7. The process of claim 1, wherein the process is effective to remove at least 95% of at least one heavy metal in the liquid wastewater.

8. The process of claim 1, wherein the pH of the liquid wastewater is reduced before the contacting step, to lower the pH of the solid mineral oxide mix during its contact with the liquid wastewater, to increase the effectiveness of heavy metal removal.

9. The process of claim 8, wherein the pH of the liquid wastewater is reduced to from about 2 to about 3.

10. The process of claim 1, wherein the mix comprises calcined bauxite residue (CBR) and further comprising processing in a furnace the solid mineral mix residue after it has been contacted with the wastewater, to reduce its oxide content and recover metallic iron.

11. The process of claim 10, wherein the furnace process comprises reducing the solid mineral mix residue with a reducing agent at a temperature of from about 500°C to about 600°C.

12. The process of claim 11, wherein the reducing agent comprises a source of solid carbon.

13. The process of claim 1, further comprising adding a coagulant to the wastewater, wherein the coagulant comprises calcium oxide.

14. The process of claim 1, further comprising washing the solid mineral oxide with acid before the contacting step, to reduce levels of at least one of Na and Ca in the solid mineral oxide.

15. A wastewater treatment process, comprising: providing a mix of solid mineral oxides that comprises calcined bauxite residue (CBR); contacting the solid mineral oxide mix with liquid wastewater that contains at least one heavy metal, wherein the solid mineral oxide mix removes at least some of the heavy metal from the wastewater; and processing in a furnace the solid mineral oxide mix after it has been contacted with the wastewater, to reduce its oxide content and recover at least metallic iron; wherein the process is effective to remove at least some of one or more of cadmium, chromium, arsenic, and mercury in the wastewater.

16. The process of claim 15, further comprising washing the solid mineral oxide with acid before the contacting step, to reduce levels of at least one of Na and Ca in the solid mineral oxide.

17. The process of claim 15, wherein the process is effective to remove at least some of one or more of cadmium, chromium, arsenic, and mercury in the wastewater.

18. The process of claim 15, wherein a ratio of solid to liquid in the contacting step is at least 1 : 10.

19. The process of claim 15, wherein the furnace process comprises reducing the solid mineral mix residue with a reducing agent at a temperature of from about 500°C to about 600°C.